The present invention relates to a roll for rolling mill which can attain the precision of strip thickness in the width-wise direction of a strip and which can control various complex profiles of strips.
In FIG. 1 is shown a most conventional four-high rolling mill comprising backup rolls a and work rolls b. The four-high rolling mill is disadvantageous in that when a strip d is rolled whose width is shorter than the length of the work rolls b, the work rolls b are curved or bent as indicated by two-dot chain lines e so that the crown of the rolled strip is increased. In order to prevent the crown from being increased, there has been employed a method in which the work rolls have a crown.
There has been also employed a method in which the crown of the work rolls is controlled. That is, as shown in FIG. 2, a sleeve g is fitted over a roll core f and an oil chamber h is formed at the center portion of the roll core f; oil under high pressure is forced into the oil chamber h so that the sleeve g is expanded and consequently the crown of the roll is controlled. However, as shown in FIG. 3, the sleeve g which is made into contact with a mating roll i is caused to bend or deflect and high stresses are developed at portions j. Therefore such rolls are adapted to be used in a cold rolling for rolling a strip under a low rolling force, but are not adapted to be used in a hot strip mill or plate mill which rolls the strip under a high rolling force.
There has been also used the so-called bending control method in which forces in the opposite directions are exerted to the shafts of the work rolls b. This method is disadvantageous in that bending is prevented at portions A of contact between the work roll b and the backup roll a so that no satisfactory result cannot be attained. As a result, a correct cross section profile cannot be obtained (See FIG. 1).
In order to solve the above and other related problems, there have been proposed various methods. One example is to axially offset intermediate rolls c in a six-high rolling mill as shown in FIG. 4. The above problems have been satisfactory overcome by this method, but new problems have arised. That is, the number of rolls is increased and the pressure distribution at the surfaces of contact become nonuniform in the axial directions of the rolls. Furthermore the maximum value of such pressure is considerably increased so that wear of the rolls is enhanced, resulting in increase of the roll maintenance cost. Moreover the housing becomes high so that is is easily lengthened due to load. In addition, since the intermediate rolls are offset in their axial directions, the rolls are damaged. The six-high rolling mill is symmetrical about the center point in construction so that when the strip d is deviated from the center of the rolling mill, the zig-zag movement of the strip d tends to occur very frequently. Furthermore when the six-high rolling mill is provided with only a pair of bearing boxes, it becomes difficult to roll the strip with a complex cross section profile.
It has been proposed a further improvement. As shown in FIG. 5, both ends of a backup roll a are chamfered so that the end portions of the work rolls b and the backup rolls a are out of contact with each other. According to this method, a strip with a relatively small width can be satisfactorily rolled; but when a strip with a relatively large width is rolled, the work rolls are not positively backed up at their portions which are in contact with side edge portions of the strip so that the side edge portions of the rolled strip are increased in thickness, resulting in formation of a negative crown.
In view of the above, the present invention has for its object to provide a roll for a rolling mill which can substantially overcome the above and other problems so that the correct cross section profile can be obtained and the rolling efficiency can be improved.
The above and other objects, effects and features of the present invention will become more apparent from the following description of the preferred embodiments thereof taken in conjunction with the accompanying drawings.